var sw = 20, //一个方块的宽度
    sh = 20, //一个方块的高度
    tr = 30, //行数
    td = 30; //列数

var snake = null; //蛇的实例
var food = null; //食物的实例
var game = null; //游戏的实例

//方块构造函数
function square(x, y, classname) {
    // 0, 0         0, 0
    // 20, 0        1, 0
    // 40, 0        2, 0

    this.x = x * sw;
    this.y = y * sh;
    this.class = classname;

    this.viewContent = document.createElement("div"); //方块对应的DOM元素
    this.viewContent.className = this.class;
    this.parent = document.getElementById("snakeWrap"); //方块的父级，并添加到页面

}
square.prototype.create = function() { //创建方块DOM
    this.viewContent.style.position = "absolute";
    this.viewContent.style.width = sw + "px";
    this.viewContent.style.height = sh + "px";
    this.viewContent.style.left = this.x + "px";
    this.viewContent.style.top = this.y + "px";

    this.parent.appendChild(this.viewContent);
}

square.prototype.remove = function() {
    //removeChild()  ===  从列表中删除一个项目
    this.parent.removeChild(this.viewContent);
}

//蛇
function Snake() {
    this.head = null; //存一个蛇头的信息
    this.tail = null; //存一个蛇尾的信息
    this.pos = []; //存储蛇身上的每一个方块的位置

    this.directionNum = { //存储蛇走的方向，用一个对象来表示
        left: {
            x: -1,
            y: 0,
            rotate: 180 //蛇头在不同的方向中应该进行旋转，要不始终是向右
        },
        right: {
            x: 1,
            y: 0,
            rotate: 0
        },
        up: {
            x: 0,
            y: -1,
            rotate: -90
        },
        down: {
            x: 0,
            y: 1,
            rotate: 90
        },
    }
}

Snake.prototype.init = function() {
    //创建蛇头
    var snakeHead = new square(2, 0, "snakeHead");
    snakeHead.create();
    this.head = snakeHead; //存储蛇头信息
    this.pos.push([2, 0]) //把蛇头的位置存起来

    //创建蛇身体1
    var snakebody1 = new square(1, 0, "snakeBody");
    snakebody1.create();
    this.pos.push([1, 0]); //把蛇身的位置存起来

    //创建蛇身体2
    var snakebody2 = new square(0, 0, "snakeBody");
    snakebody2.create();
    this.tail = snakebody2; //把蛇尾的信息存起来
    this.pos.push([0, 0]); //把蛇身的位置存起来

    //形成链表关系
    snakeHead.last = null;
    snakeHead.next = snakebody1;

    snakebody1.last = snakeHead;
    snakebody1.next = snakebody2;

    snakebody2.last = snakebody1;
    snakebody2.next = null;

    //给蛇添加一条属性，用来表示蛇走的方向
    this.direction = this.directionNum.right; //默认让蛇往右走
}

//这个方法用来获取蛇头的下一个位置对应的元素，要根据素材做不同的事情
Snake.prototype.getNextPos = function() {
    var nextPos = [ //蛇头要走的下一个点的坐标
        this.head.x / sw + this.direction.x,
        this.head.y / sh + this.direction.y
    ]

    //下个点是自己，代表撞到了自己，游戏结束
    var selfCollied = false;
    this.pos.forEach(function(value) {
        if (value[0] == nextPos[0] && value[1] == nextPos[1]) {
            //如果数组中的两个数组都相等，就说明下一个点在蛇身上里面能找到，代表捡到自己了
            selfCollied = true;
        }
    })
    if (selfCollied) {
        console.log("撞到自己了！");
        this.strategies.die.call(this);
        return;
    }

    //下个点是围墙，游戏结束
    if (nextPos[0] < 0 || nextPos[1] < 0 || nextPos[0] > td - 1 || nextPos[1] > tr - 1) {
        console.log("撞墙了！");
        this.strategies.die.call(this);
        return;
    }

    //下个点是食物，吃
    if (food && food.pos[0] == nextPos[0] && food.pos[1] == nextPos[1]) {
        //如果这个条件成立说明现在蛇头要走的的下一个点是食物的那个点
        console.log("撞到食物了！ ");
        this.strategies.eat.call(this);
        return;
    }

    //下个点什么都不是，走
    this.strategies.move.call(this);
}

//处理碰撞后要做的事
Snake.prototype.strategies = {
    move: function(format) { //这个参数用于决定要不要删除最后一个方块（蛇尾）。当传了这个参数后就表示要做的事情是吃
        //创建新身体（在旧蛇头的位置）
        var newBody = new square(this.head.x / sw, this.head.y / sh, "snakeBody");
        //更新链表的关系
        newBody.next = this.head.next;
        newBody.next.last = newBody;
        newBody.last = null;

        this.head.remove(); //把旧蛇头原来的位置删除
        newBody.create();

        //创建一个新蛇头（蛇头下一个要走到的点nexpos）
        var newHead = new square(this.head.x / sw + this.direction.x, this.head.y / sh + this.direction.y, "snakeHead");
        //更新链表的关系
        newHead.next = newBody;
        newHead.last = null;
        newBody.last = newHead;
        newHead.viewContent.style.transform = "rotate(" + this.direction.rotate + "deg)"
        newHead.create();

        //蛇身上的每一个方块的坐标也要更新
        this.pos.splice(0, 0, [this.head.x / sw + this.direction.x, this.head.y / sh + this.direction.y, ]);
        this.head = newHead; //还要把this.head的信息更新一下

        if (!format) { //如果format的值为lafse，表示需要删除（除了吃之外的操作）
            this.tail.remove();
            this.tail = this.tail.last;

            this.pos.pop();
        }
    },
    eat: function() {
        this.strategies.move.call(this, true);
        createFood();
        game.score++;
    },
    die: function() {
        game.over();
    }
}

snake = new Snake();

//创建食物
function createFood() {
    //食物小方块的随机坐标
    var x = null;
    var y = null;

    var include = true; //循环跳出的条件，true表示食物的坐标在蛇身上（需要继续循环）。false表示食物的坐标不在蛇身上（不循环了）
    while (include) {
        x = Math.round(Math.random() * (td - 1));
        y = Math.round(Math.random() * (tr - 1));

        snake.pos.forEach(function(value) {
            if (x != value[0] && y != value[1]) {
                //这个条件成立说明现在随机出来的这个坐标，在蛇身上并没有找到。
                include = false;
            }
        })
    }
    //生成食物
    food = new square(x, y, "food");
    food.pos = [x, y]; //存储一下食物生成的坐标，用于跟蛇头要走的下一个点做对比

    var foodDom = document.querySelector('.food');
    if (foodDom) {
        foodDom.style.left = x * sw + "px";
        foodDom.style.top = y * sh + "px";
    } else {
        food.create();
    }
}



//创建游戏逻辑
function Game() {
    this.timer = null;
    this.score = 0;
}

Game.prototype.init = function() {
    snake.init();
    // snake.getNextPos();
    createFood();

    document.onkeydown = function(ev) {
        if (ev.which == 37 && snake.direction != snake.directionNum.right) { //用户按下左键的时候，这条蛇不能是正下往右走
            snake.direction = snake.directionNum.left;
        } else if (ev.which == 38 && snake.direction != snake.directionNum.down) {
            snake.direction = snake.directionNum.up;
        } else if (ev.which == 39 && snake.direction != snake.directionNum.left) {
            snake.direction = snake.directionNum.right;
        } else if (ev.which == 40 && snake.direction != snake.directionNum.up) {
            snake.direction = snake.directionNum.down;
        }
    }

    this.start();
}
Game.prototype.start = function() { //开始游戏
    this.timer = setInterval(function() {
        snake.getNextPos();
    }, 200);
}

Game.prototype.pause = function() {
    clearInterval(this.timer);
}

Game.prototype.over = function() {
    clearInterval(this.timer);
    alert("你的得分为：" + game.score);

    //游戏回到最初的状态
    var snakewrap = document.getElementById("snakeWrap");
    snakewrap.innerHTML = "";

    snake = new Snake();
    game = new Game();

    var startBtnWrap = document.querySelector(".startBtn");
    startBtnWrap.style.display = "block";
}

//开启游戏
game = new Game();
var startBtn = document.querySelector(".startBtn button");
startBtn.onclick = function() {
    startBtn.parentNode.style.display = "none";
    game.init();
}

//暂停
var snakewrap = document.getElementById("snakeWrap");
var pauseBtn = document.querySelector(".pauseBtn");
snakewrap.onclick = function() {
    game.pause();

    pauseBtn.style.display = "block";
}

pauseBtn.onclick = function() {
    game.start();
    pauseBtn.style.display = "none";
}
